Process for purification of metals.



PATENTED JUNE 23, 1908.

C. T. KNIPP. PROCESS FOR PURIFICATION OF METALS.

APPLICATION FILED AUG. 6. 1907.

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ROE HT- LEHDs Fnofl sou OF ELEOTRRQ CURRE WITNESSES.-

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CHARLES Tl KNIPP, OF URBANA, ILLINOIS.

PROCESS FOR PURIFICATION OF METALS.

Application filed August 6, 1907. Serial No. 387,871.

Specification of Letters Patent.

- Patented June 23, 1908.

To all whom it may concern:

Be it known thatI, CHARLES T. KNIPP, a citizen of the United States, residing at Urbana, in the county of Champaign and State of Illinois, have invented certain new and useful 1m rovements in Processes for Purification of etals, of which the following is a specification, reference being had to. the accorfipanying drawings.

y invention relates to improvements processes for the purification of metals; and an object of my invention is to provide a process which will result in removing practically all the im urities from the metal and which will be slmple, economical and eflicient.

The mercury still described in my pending application Serial No. 329 ,619 filed August 7,

1906, is one form of apparatus for carrying out my new process.

As applied to the urification of the metal, mercury, for examp e, my new process'consist-s in vaporizing the metal by. an electric arc and in vacuo; and then condensing the vapor out of contact with the impure metal and leading away the distillate.

hausti ble.

The mercury is se arated into two portions which in the sti 'form the electrodes of an electric arc,'the pressure upon the mercury being reduced as far as possible. by exthe air from the still as far as possi- T e heat from the electric arc volatilizes the mercu and the mercu vapor flows into an t iler chamber of t e still,

known as the condensing chamber, and is there condensed out of contact with the'imtion is s own in the drawing, m which pure mercury. The distillate flows from the condensing chamber-and -passes through a capillary tube connected therewith, whereby the vacuum in the still is maintained; but it is not to be understood that this air-pump action of the distillate is an essential step in my new process, for the vacuum 'may be maintained by other well-known means.

An a paratus for carryingout m 'y inven- Fi re 1 is an elevation of the ap aratus and i s. 2 and 3 illustrate modi cations hereina ter referred to.

.The ends of the tube A are bent downwardly and formed with the bulbs B, C from each ofwhich extends a small bore' tube D, the lower-end of which di s into a vessel E. Intermediate the bulbs 1;, C the tube A is formed with a recess or pocket F in the bottom of which isfused a platinum wire G for a pur ose hereinafter referred to.

7 e tube A is in communication with (opens into) one end of the condensation tu e H the other end of which is extended downwardsby the tube I'which terminates in an S provided with an enlargement or resis of comparatively arie bore, while the lower portlon I of the tu e I isof small bore, or a capillary tube. Between the portions I and I is an enlargement or chamber S within which is a hollow valve S, which prevents any flow of mercury from the reservoir S into the capillary tube 1' except through the valve itself. From near the top of the valve S extends downwardly a tubular inlet arm 72. which reaches to near the bottom of the chamber S; and extending upwardly from the valve is a vent-piece 12 which permits air to be exhausted from the capillary tube 1' through the yalve S. The latter traps the mercury'in the bulb S; and when the mercury has reached the level of the point of junction of the arm or inlet tube It with the top of the valve S, the mercury will escape through the valve S into the capillary tube 1'. In this way any dross or impurity floating on the to of the mercury in the chamber S is prevente from escaping into the capillary tube I.

The condensation tube H is provided with the condensation chamber K and is formed with a nipple L for the attachment of a rubber hose or like means of connection to a Geryk hand or power air-pump (not shown), or other equally effective air-pump.

The'upper portions of the tubes D and I are made separate from their lower portions as is indicated at U, U U. This construction enables the upper art of the apparatus to be separated from t e lower part, for the purpose of cleaning. When the'apparatus 1s m useythe spaces U, U U are ridged over or closed by a piece of rubber tubing r. When the tubing is new, it will be found generally to suffice in keeping the joints airtight. In order to reinforce the tubing 1' and hermetically seal the joint, a jacket made up of a cork c and .tube t filled with mercury m- 1s used. Although only one of the joints (that marked U) is shown fitted with this fermeture, it will be understood that the other two joints U, U" are also sealed, when the apparatus is in use.

The mercury in one of the vessels E is conervoir J. The upper ortion I of the tube I nected with the negativr pole of a suitable source of electric current, as a dynamo, storage battery or the like. Preferably direct current is used. The mercury in the other vessel E is electrically connected through the resistance R with the positive pole of the source of electric current and with this same positive pole the platinum wire G of the side connection F is connected through the resistanceR. Of course, it will be understood that the mercury in the tubes'D and the bulbs B, F and C serve as conductors for the electric current The mercury in the bulb G acts as a return circuit for the current which flows through the mercury in the bulbs B and F.

The length of the capillary portion I of the tube I is such that the level of the column of mercury sustained by the atmosphere in thecapillary tube I is about five centimeters below the bottom of the chamber S. The volume of the bulb J is sufficient to insure against the admission of air.

The vessels E are made with their upper portions wideand shallow or dish-sha ed,

' and resemble somewhat a frying pan rom -which extends downwardly a pi e.

This shape enables the vessels E to ho d a large volume of mercury without altering in a reat degree the mercury level in the bulbs B and C.

To start the still: Place a beaker E of clean mercury at the lower end of the tube I allowing the latter to di into it, as shown by the dotted outline. P ace the vessels E in position as shown and fill with the mercury to be distilled. Connect the nipple L to an airpump, (a Ger k hand or power ump is well adapted for t is pur ose), and s owly exhaust the air from the sti l. The mercury will rise in the tubes I and D, and after 15 or 20 minutes of pumping, it will become stary t e columns of mercurytiona'ry. Clea are supported b the ressure of the atmosphere. Now a just t e position of one of the vessels E until the mercury stands in the bulb B at the level indicated in the drawing. Next raise the other vessel E, until the mercury rises in the bulb C and overflows, filling the pocket F, after which the vessel E is lowered so that the column stands in the bulb C at the level indicated by the heavy shading. The volume of the bulb J is sufficient to insure against the admission of air, hence, the beaker E at the lower end of I may now be lowered to the osition indicated by the full line sketch. Electrical connections are now made as indicated in the drawing. There is a divided circuit, one branch of which includes the resistance R and the mercury in the bulb B, while the other branch includes the resistance R and the mercury in the pocket F; the common return for-the two branches is the mercury in the bulb C. The side connection F is purely to start the senses are between the electrodes B and C as de-' scribed by Weintraub, Phil. Mag., Vol. VII, February, 1904, but the arc may be started quite readily by dis ensing with the side connection F and simp y raisin the level of the mercury columns in the bu bs B and C by raising the vessels E until the two columns touch, and then lowering the vessels. Or it may be started by the method of using a high otential discharge, as originally used by lewitt and others.

After the arc is once started between the bulbs B and C (by the Weintraub method), the circuit through the side connection F is broken. The mercury vapor fills the tube A, the tube H and the condensation bulb or chamber K, upon the walls of which it condenses. The shape and position of the tube H and the condensation chamber K are such that the condensed mercury is diverted into the tube I and thence is discharged through the valve S into the beaker ll placed to re ceive the distillate as shown in the full lines in the drawing. As the purified metal falls drop by drop through the capillary tube I, it operates as in an air-pump of the Sprengel type and tends to maintain the vacuum produced by the Ger k pump used in starting the ap aratus. owever, experience indicates tl at it is advisable to operate the latter pump from time to time, especially if the impurities ive ofl gases, as they are very liable to do. f desired, the tube may be made of the same bore throughout, the bore being the same as that of the upper portion I, in which case the chamber S 1's omitted but the S- shaped end and the bulb J are retained. (See Fig. 2, in which I is the tube). In this case the dropping of the purified mercury will not operate to maintain the vacuum. Again, the discharge of the urified mercury may be made to take place t rough a straight tube I, (Fig. 3), dipping into a vessel, as do the tubes D into the vessels E.

The theory underlying the hereinbefore described rocess may be stated as follows: It is well known that a metal in the liquid state, 6. g., mercury, gives off a vapor to a greater or less extent. The amount of vapor given off depends upon the temperature and uplon the pressure,being excessivel small w en the tem erature of theliquid 13 little above the me ting point of the metal. Let us consider the case when the pressure is kept constantwhen the liquid metal is contained in an 0 en dish. The pressure is that of the atmosp ere. The amount of metal vapor given off will steadily increase as the temperature is raised until the boiling point is reached when there will be a great evolution of vapor. At this point, as is the case of non-metallic liquids, the temperature remains constant until all of the li uid is vaporized. The addition of more eat simply hastens the vaporization without rise in temperature. Now consider the case when the temperature is kept constant and the pressure varied. To realize this case the liquid is placed in an inclosure connected to a pump capable of increasing or decreasin the pressure at will within the vessel. 1% the pressure is increased, the amount of vapor given off is lessened, while if the pressure is decreased, the vessel is exhausted, the amount of vapor given ofl is increased. If the exhaustion is carried to completion, nothing i but metallic vapor remains in the inclosure.

If now, in addition, heat is supplied to the vessel, it will be found in general that but little rise in temperature is necessary to cause a great evolution of va or. In other words, aliquid (either metallic or non-metallic) will boil, and consequently evolve its vapor at a much reduced temperature, if the pressure is reduced. This theory is directly ap licable to the process in question. The

sti 1 being well exhausted of air means that the mercury vapor will be given oft copiously at a much lower temperature than it would be where the mercury is boiled at atmospherical pressure. The lower the temperature under which the still operates, the less liable are the impurities, such as zinc, copper, lead, etc. that are held in solution by the mercury, to be carried over into the distillate. These impurities, and others that may be found, all have melting'points considerably above the boiling point of mercury in air. If the mercury is boiled in a partial vacuum or a nearly perfect vacuum, the chances of the impurities being carried over are much less; because, as pointed out above, the

amount of vapor given off by a solid metal is,

proportional to the temperature, which in the case assumed is com aratively low.v

In the process herein efore described, a vacuum is necessary for two reasons, (a) to ,maintain the are, and (1)) because a high vacuum means a low temperature at whichthe mercury is vaporized.- If the vacuum is not high, the temperature .of the-arc rises rapidly .and the hlgh temperature tends to vaporize the impurities. The temperature as registered by a co perlatinum thermocouple placed Within t e st at the mouth of 'thecondensing chamber is about 160 degrees centigrade when the still is run at the normal rate. The temperature of boiling mercury in air is 360 degrees centigrade.

The action of the current flowing throu h the still is not only to heat and vaporize t e mercury but the electric forces lonize the mercury va or as well. The complete rocesses that t e vapors within the' still un ergo are not fully understood, especially when there are vapors of various metals, (in this case considered impurities) present. That there is a suppressive action on the, say zinc, ions is evident when a com arative study of the various methods is ma e. It was found by tests of great refinement that the 'distil late produced by my new process for a given sample of mercury that was slightly impure to zinc was of much greater purity than the distillate from any of the other approved low pressure stills that have been recently described. This hi her. degree of purity may be ascribed to it) the low temperature that obtains in the mercury are still; (1)) the ionization processes within the tube; and (c) the high vacuum that is necessary to maintain the arc.

This application is filed as a divisional application which claims the process described as being carried outby the a Iparatus claimed in my pending application erembefore referred to.. a

I claim: 1. A process for the purification of metals COIISIStIIIg-JII generating an electric are between two portions of the metal to be urified under a pressure lower than that o the atmosphere, thereby vaporizin the metal; and condensing the vapor pro uced out of contact with the im. ure metal.

2. A process for t e purification of metals consisting in generating anelectric are between two portions of the metal to be urij fled under a pressure lower than that o the atmosphere, thereby vaporizing the metal; condensing the vapor produced out of contact with the impure metal; and maintaining the low ressure upon the impure metal by leading t e distillate away. drop by drop.

In witness whereof I have hereunto set my hand in the presence of .the two undersigned witnesses at said Urbana this second day of August,'- 1907.

CHAS; 'r. KNIPP Witnesses: LEWIS A. MCLEAN, "L. E. GAILEY. 

